Update compiler-builtins submodule

This commit updates our `compiler-builtins` submodule which brings in at
least a few improvements for intrinsics on wasm32

diff --git a/src/libcompiler_builtins b/src/libcompiler_builtins
index 0703bfa72524e01e414477657ca9b64794c5c1c3..939cbca6e9d829265d6cf006d3532142a4061cd3 160000 (submodule)
--- a/src/libcompiler_builtins
+++ b/src/libcompiler_builtins
@@ -1 +1 @@
-Subproject commit 0703bfa72524e01e414477657ca9b64794c5c1c3
+Subproject commit 939cbca6e9d829265d6cf006d3532142a4061cd3